In modern and future (cellular) communication systems, an inter-band multi-carrier capability of devices such as terminal devices is gaining more attention and importance.
For example, in 3GPP systems, inter-band carrier aggregation represents an inter-band multi-carrier communication framework which shall be supported by devices such as terminal devices. In inter-band carrier aggregation, at least two carriers operating on different (frequency) bands are aggregated together in/for at least one of downlink and uplink.
When multiple carriers operating on different (frequency) bands are combined or aggregated, such as in inter-band carrier aggregation, intermodulation distortion (IMD) is typically produced due to nonlinearity in active and/or passive components of a device transmitter (in case of uplink transmission), a device receiver (in case of downlink transmission) or a device transceiver (in both cases). Generally, intermodulation distortion components of (m+n)-th order are located at frequencies m*f1±n*f2. For instance, assuming that uplink carriers/bands at frequencies fUL1 and fUL2 are combined or aggregated, a second order intermodulation distortion component is located at one of frequencies 2*fUL1, 2*fUL2, and fUL1±fUL2, and a third order intermodulation component is located at one of frequencies 3*fUL1, 3*fUL2, 2*fUL1±fUL2, fUL1±2*fUL2, and so on. Further, harmonic distortion is also produced, which is located at a frequency x*fUL for xt-th order harmonics of an uplink carrier/band at frequency fUL.
When at least one (or part) of such intermodulation distortion components and/or at least one (or part) of such harmonic distortion components falls in a (frequency) band being used for some transmission operation by the device in question, e.g. a DL carrier/band, such distortion can cause a significant amount of desensitization. Such desensitization is specifically applicable for certain (inter-band) combinations of standardized carriers/bands depending on one or more of the frequency relations between uplink and downlink channel definitions, antenna operational conditions and antenna isolations.
Namely, for certain frequency relations between uplink and downlink channel definitions, (part of) intermodulation distortion components of uplink carrier/band combinations and/or (or part) of harmonic distortion components of uplink carriers/bands hit on top of a downlink carrier/band and thus destroy the performance thereof, if no additional power restrictions are in place. Referring to 3GPP uplink and downlink channel definitions according to 3GPP TS 36.104 (Table 5.5-1), for example, aggregating bands (i.e. aggregating component carriers operating on bands) B20 and B8 causes a third order intermodulation distortion component from B20 UL (832-862 MHz) and B8 UL (880-915 MHz) to overlap with B8 DL (925-960 MHz). As another example, a third order harmonic distortion of B17 UL (704-716 MHz) overlaps with B4 DL (2110-2155 MHz).
Furthermore, (part of) intermodulation distortion components and/or (or part) of harmonic distortion components can also hit on top of some non-3GPP Radio Access Technology (RAT), for instance in the 2.4 GHz frequency band (ISM band) used e.g. by WLAN and Bluetooth. For instance, this is the case for the second order intermodulation distortion component when aggregating bands B4 and B12.
The distortion problem as outlined above, i.e. an excessive desensitization of some operating band/carrier (e.g. a DL carrier in case of a multi-band UL carrier combination and/or UL band harmonic), can be avoided if the distortion power of a distortion component is sufficiently low as compared with the actual transmission power of that operating band/carrier. For instance, under current assumptions, desensitization could be considered to be not significant when being smaller than 0.5 dB.
In order to ensure an acceptable level of desensitization, power restriction values are adopted, which define relaxation to maximum output power of one or more UL bands of a terminal device. As such output power relaxation adversely affects the coverage of the terminal device, the power restriction values are to be specified in view of a tradeoff between DL distortion or desensitization and device UL coverage.
In 3GPP standardization, power restriction values are defined under rather pessimistic assumptions in terms of reference architecture and values for component performance so as to reliably ensure that real implementations based on such values are practicable, while still meeting requirements for desensitization (e.g. a maximum allowable desensitization of 0.5 dB). Accordingly, such standardized power restriction values are not very strict, and deviate from achievable implementations (which could meet required desensitization performance with lower power restrictions).
That is to say, for the benefit of meeting desensitization requirements, standardized power restriction values excessively restrict device UL coverage, thus taking a loss in suboptimal device UL coverage. However, there are currently no means for reliably and efficiently ensuring an appropriate tradeoff between DL distortion or desensitization and device UL coverage in view of standardized power restriction values.
Thus, there is a desire to provide for power restriction control for inter-band multi-carrier capable devices. More specifically, is a desire to provide for power restriction control for inter-band multi-carrier capable devices in terms of a tradeoff between distortion or desensitization and device coverage, e.g. in the context of inter-band carrier aggregation.